It will be only for a few seconds. The 5C will only be drawn under heavy acceleration which should only last a few seconds.
The original engine can produce 147kw. That would equate to 2C and it would accelerate 0 to 100kph in 15sec. So at 5C it would take 6sec. So unless it was accelerating really hard on a very steep and long hill I doubt 5C will be required for more than a few seconds.
Also during those 6sec it is only towards the top speed that the 5C will be required. So the average over the 6sec acceleration will be less than 5C.

I didn't think you would be pulling 5c in the real world much, to my ears I thought you were going to try to run a 12minute test at 5c(ie all the capacity) , which would be a lot of energy to sink.
If you are planning to run a 10 sec test, maybe a carbon pile load tester. Most should be good for 500- 1000a for 15 seconds

I need to run at the maximum the cell is rated, run water thru the cooling system and check battery temp and get some data for the efficiency of the cooling system . So potentially it may run for 12min if the cooling system is really good.

I run a cooling system test yesterday.
The test was designed to see how effective the cooling system was at coupling the coolant and the cells. I run the pack at 220A (1.16C the battery is 189Ah) until fully discharged.
The cooling system did not have a radiator. It just had a bucket of water (about 5lt of water). The idea was to measure the temperature raise in the water to determine how well the energy was being removed. This ensured that I would have some idea of how much energy the cooling system could remove.
The starting temperature of the water and cells was 24C. I placed several temperature sensors to get a measure of the temperature difference between the coolant and the cell surface.
This picture shows the location of the sensor.
The end temperature after the test which took about 50min to empty the battery was 38C for the batteries and 37C for the water in the bucket.
Here is a picture of the bucket. I had a hose for each tube so I could confirm that all cooling pipes would flow the same amount of liquid.
Here is a picture showing where the sensors were attached.
The packs internal resistance is 5mOhms at 220A the whole pack would dissipate about 240w.
After the test was finished I run cold water (24C) thru the cooling system and it took 3min for the batteries to get back to 24C (all the thermometers to read 24C)
I will run a test at 3C and maybe 5C later and will run cold water thru the system to see how well it handles the extra power.

Does any one know how this compares to a Tesla battery pack?
I have been looking for data on the Tesla packs but I can not find anything that shows temperature difference between coolant and battery.

[ Edited Coulomb: side by side "corrected" image addresses (may not be permanent) ]

I run the 2C test today and the results were as follows:
Output current 380A
Starting water temperature 24.5°C
Starting pack temperature 27°C
Test run for 10min. Could not run longer because output cable started to overheat. (Smoke started to come out)
Cell temperature after 10min was 35°C water temperature 30°C
We were adding removing some water and replacing it with fresh water to try to keep the water under 30°C. At the end of the test the cell temperature had already stabilised.
The tabs were getting quite hot they got to around 45°C but the cell temperature near where the tab went in as a little hotter but the rest of the cell was cool to the touch. After the current was turned off the tabs cooled down very quickly which leads me to think that the heat from the tabs was generated by the contact resistance.
The temperature difference between the cells and the water was 5°C which is close enough to 4 times the difference to the 1C test. The 2C test Should have 4 times the energy loss on the cells as the 1C test. So everything seems to add up.

Thanks for sharing the progress. You really should run the Battery Test Centre technical team. Some of the results are riddled with technical issues (due to difficulties interfacing with BMS, whether OEM or non-OEM)

I have some data on Tesla packs somewhere I can share, and I also have the mass flow calculations for heat flux out of the battery. I will see if I can get them into an easily shared format first.
Chris

I have been trying to do some high current testing of the battery module but I have been having some problems with the connections to the cells overheating. I am very confident it is the cell connections because when I turn the load off the connections cool down very quickly and when I turn the cooling off after turning the power off the cell temperature does not go up. Also some connections are hotter than others. So this leads me to think that the inside temperature of the cells is not substantially higher than the outside and the high temperature of the tabs is not coming from the inside of the cell.
I have messed around with the tab clamps and I think I got something working.
The last test on the battery module was as follows:
Staring cell temperature 29°C.
Starting water temperature 26°C. Water volume about 5lt.
Test current 380A (2C).
Output power 13.9kw
The test run for only 10min because the 35mm2 wires from the battery to the load resistor started to overheat.
End cell temperature 35°C.
End water temperature 29°C.
Water was not refreshed and did not run thru a radiator.

I am hoping to run a 2C discharge test until the battery is fully discharged to see if the cooling system can keep the batteries below 45°C for the entire duration of the test.

The cell tab is the highest resistance point in the cell, and it's typically the hottest single point in the circuit. A solid buslink here is critical to ensuring the cells don't get too hot. The paper attached above looks into cooling the cell terminations as a means to keeping the whole cell cool. Makes sense as the tab has direct metal conductivity to the source of the heat. It does create a difficult situation in that the conductors can't be cooled directly (galvanic isolation is required).

The cells will last a long time if maintained at or around 20'C for the entirety of their life. Even if they do get hotter than this, the key is ensuring they don't spend very long at that temperature - so make sure the cells return to an ambient temperature as quickly as possible.

I hope to set up a discharge test of my battery tonight, and I'll plot the findings.

I just finished doing another 2C test.
This time I managed to keep the test going until the pack was discharged. The results are as follows:
Test current 400A
Initial cell temperature 27°C (weather is getting hot )
Initial water temperature 25°C

End water temperature 28.6°C (I had to change the water twice because it was getting too hot)
End cell temperature 37°C

So I can safely say that at I can run the cells at 2C continuously without overheating.
I guess if I could keep the water at 25°C (which is the plan) I should never overheat the batteries.
I also assume that I shouldn't have any problems running at 5C for very short bursts as the internal cell temperature would be quite cool to start with.

Hi Francisco,
Thank you for presenting your project on our AEVA meeting yesterday.
It was great to see your progress and very interesting solutions of some problems.
Great idea!!! and very impressive work!!! Well done.!!! You have impressed quite a few people if not all of us.
You are a really very brave man to take a challenge like this one.
Wishing you not to many troubles before you finish.
Kind regards. Marek.

Thank you for listening to my talk at the meeting.
I have been a little busy so I did not have time to upload pictures.
Here are some picture updates.
These are pictures of the load resistor that I used for the 2C test.
The resistance is 0.8Ohms
It is made of packing steel belt and immersed in running water.
It has already rusted because it has been in the water a few days. It has 4m of 16mm steel belt.https://photos.app.goo.gl/128aKXVp898whWKj7https://photos.app.goo.gl/evAueVpgup1EhEsc8

It has been a long time since my last post. I have been a little busy and I was waiting for the pictures issue to fix sorted. It seems it has.
The following pictures are from around 22-Dec 2018.
I got the last parts for the gear box and the bus bars for the inverter.
Here are some pictures of the front of the motor where the gear box goes:

20181218_111845.jpg (130.03 KiB) Viewed 426 times

The bolts are not the right ones. I just did not have the right length ones at the time.
This is the back where the inverter goes.

20181218_111833.jpg (194.35 KiB) Viewed 426 times

This is the motor bolted to the back diff. More or less how it will go. I just have to make the brackets.

Looking at the area of the floor of the battery, you will want a fairly strong material. I'm using that honeycomb sandwich material for the battery floor of the Prelude, but it's a lot of trouble - I wouldn't recommend it. But maybe the Dibond aluminium / polyethylene with appropriate beams would work OK?

I am planning to put some beams like the angle holding the mockup. The beams will be bolted to the underside. There are already a few holes with threads in the frame so I will not have to weld or cut anything to the original chassis. The battery modules are very strong so they will not need too many bracing points so the case doesn't really have to be structurally strong.
Because it is a 4WD I was thinking of using a thin case (maybe 2mm Al or maybe HDPE) just to keep a water tight enclosure and have a steel bash plate under that.
I haven't really got to that part yet so still open for ideas.
I am trying to keep the bottom about the same height as the bottom edge of the body so with a bit of luck I will end up with more if not the same ground clearance as original so I need the case to be as thin as possible.

Here are some pictures of the center battery module.
The battery will have 3 separate modules as in the picture below.

Battery CAD drawing.JPG (95.44 KiB) Viewed 316 times

I have almost finished the center module. I have been doing the center module just to make sure that I can assemble the pack and that the design is mechanically sound and it can be assembled.
I have had to assemble and reassemble the pack about 5 times before I finally got everything to work ok. Mostly I have been having to make jigs so when I assemble the module everything is in the right place and everything lines up. Everything has to line up to about 1mm so that it can be assembled.

The module is 20S3P, 189Ah. It holds 14kwh and the nominal output voltage is 72v.
I have not had a chance to weigh it yet but I expect it will be around 68kg.
I am still missing some of the connectors that connect the end manifold to the cooling pipes. I hope to get them on Mon next week.
I am planning to bring the battery module to the meeting on Wednesday if any one wants to have a look.

Yes about the 14kw. It should have been 14kwh. Only the center pack is 14kwh the ones on the sides are bigger. The side ones are a little under 30kwh each. The center pack has 20 3P cells the entire battery has 103 3P cells.
I have measured the 14kwh at a discharge rate of 1C starting at 4.2v and finish at 3.2v per cell and not all the cells get to 3.2v at the same time and not all of them start at 4.2v. The datasheet says the cells can go down to 3v but i think it is best to not get too low.
The BMS I am using for the test does not do balancing I just use it to measure the cell voltages. Once I get the active balancing BMS I expect I could get a bit more. So I expect I would be able to get 14kwh of useable storage out of the center pack.